Group III nitride substrates are increasingly valued for their usefulness in preparation of electrical components. For example, Group III nitride based semiconductors have become a leading material for use in the production of light emitting diodes (LEDs), particularly blue and white LEDs and blue laser diodes, as well as high-power, high-temperature electronics. While Group III nitride substrates have proven extremely useful and versatile, they have also proven somewhat difficult to prepare.
Epitaxial methods can be hindered by the lack of a single crystal Group III nitride substrate, or other high quality single crystal substrates, with the same lattice parameters as the Group III nitride film to be grown thereon. Epitaxial growth of nitrides is often performed on sapphire or silicon carbide substrates. Even with such substrates, though, it can be difficult to provide a substrate having a surface in a condition for optimal film growth. Aluminum nitride substrates can be particularly useful substrates in epitaxial methods; however, AlN substrates cannot typically be stored for long periods of time because of the ease of surface reaction between aluminum and atmospheric oxygen or moisture.
The surface condition of a substrate can be particularly related to the later usefulness of the substrate for thin film growth. For example, surface preparation can influence the nucleation stage of thin film growth and, consequently, the growth morphology of the film. This in turn can determine the electrical and optical properties of the grown film, which is particularly important since these properties need to be well controlled for the fabrication of electronic and optoelectronic devices.
Given the usefulness of the Group III nitride films, and components incorporating such films, it is desirable to have a method for forming a protective layer on aluminum nitride substrates to ensure the substrates remain in optimal condition for later film growth. It is also desirable that such protective layers be easily formed and easily removed. Such methods, as well as aluminum nitride substrates useful in the growth of Group III nitride films, are provided according to the present invention.